 /*******************************************************************************
  * Copyright (c) 2000, 2004 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.core.internal.runtime;

 import java.io.*;

 /**
  * Decrypts a stream of data that was encrypted using the
  * <code>Cipher</code> or <code>CipherOutputStream</code>.
  *
  * @see Cipher
  * @see CipherOutputStream
  */
 public class CipherInputStream extends FilterInputStream {
     private static final int SKIP_BUFFER_SIZE = 2048;
     private Cipher cipher;

     /**
      * Constructs a new <code>CipherInputStream</code> that decrypts the
      * data in the given <code>InputStream</code>. The data can only be
      * decrypted if the given password is the same as that which was used
      * to encrypt it.
      *
      * @param is
      * @param password
      */
     public CipherInputStream(InputStream is, String password) {
         super(is);
         cipher = new Cipher(Cipher.DECRYPT_MODE, password);
     }

     /**
      * @see InputStream#markSupported()
      */
     public boolean markSupported() {
         return false;
     }

     /**
      * @see InputStream#read()
      */
     public int read() throws IOException {
         int b = super.read();
         if (b == -1)
             return -1;
         try {
             return (cipher.cipher((byte) b)) & 0x00ff;
         } catch (Exception e) {
             throw new IOException(e.getMessage());
         }
     }

     /**
      * @see InputStream#read(byte[], int, int)
      */
     public int read(byte b[], int off, int len) throws IOException {
         int bytesRead = in.read(b, off, len);
         if (bytesRead == -1)
             return -1;
         try {
             byte[] result = cipher.cipher(b, off, bytesRead);
             for (int i = 0; i < result.length; ++i)
                 b[i + off] = result[i];
             return bytesRead;
         } catch (Exception e) {
             throw new IOException(e.getMessage());
         }
     }

     /**
      * @see InputStream#skip(long)
      */
     public long skip(long n) throws IOException {
         byte[] buffer = new byte[SKIP_BUFFER_SIZE];

         int bytesRead = 0;
         long bytesRemaining = n;

         while (bytesRead != -1 && bytesRemaining > 0) {
             bytesRead = read(buffer, 0, (int) Math.min(SKIP_BUFFER_SIZE, bytesRemaining));
             if (bytesRead > 0) {
                 bytesRemaining -= bytesRead;
             }
         }

         return n - bytesRemaining;
     }
 }

